I have a friend that has reloaded for 25 years. He says he uses the larger Federal 215 primers for all of his .270 loads. What would be the benefit of using such a primer for this caliber? Is there any disadvantage or reason not to?

He only has to store one type of primer in his reloading cabinet...

Spring,

A magnum primer is not needed in a .270 unless you are using hard-to-ignite powder or hunting in sub-zero temperatures.

No benefit at all, unless possibly in temperatures below -20 degrees F!

I use cc250m and rem 9 1/2m primers for 270, 140gr spbt load. there is some increase in pressure so i reduced the load 2 grs and work back up accuracy was about the same.
velocity increased about 30f/s. using imr4064.also the brass sealed up on the neck better, not as much soot.
Dave